[PATCH 2/7] rust: kunit: support checked `-> Result`s in KUnit `#[test]`s

Miguel Ojeda
2025-05-02T21:51:57Z

Currently, return values of KUnit `#[test]` functions are ignored.

Thus introduce support for `-> Result` functions by checking their
returned values.

At the same time, require that test functions return `()` or `Result<T,
E>`, which should avoid mistakes, especially with non-`#[must_use]`
types. Other types can be supported in the future if needed.

With this, a failing test like:

#[test]
fn my_test() -> Result {
f()?;
Ok(())
}

will output:

[ 3.744214] KTAP version 1
[ 3.744287] # Subtest: my_test_suite
[ 3.744378] # speed: normal
[ 3.744399] 1..1
[ 3.745817] # my_test: ASSERTION FAILED at rust/kernel/lib.rs:321
[ 3.745817] Expected is_test_result_ok(my_test()) to be true, but is false
[ 3.747152] # my_test.speed: normal
[ 3.747199] not ok 1 my_test
[ 3.747345] not ok 4 my_test_suite

Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
rust/kernel/kunit.rs | 25 +++++++++++++++++++++++++
rust/macros/kunit.rs | 3 ++-
2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/kunit.rs b/rust/kernel/kunit.rs
index 2659895d4c5d..f43e3ed460c2 100644
--- a/rust/kernel/kunit.rs
+++ b/rust/kernel/kunit.rs
@@ -164,6 +164,31 @@ macro_rules! kunit_assert_eq {
}};
}

+trait TestResult {
+ fn is_test_result_ok(&self) -> bool;
+}
+
+impl TestResult for () {
+ fn is_test_result_ok(&self) -> bool {
+ true
+ }
+}
+
+impl<T, E> TestResult for Result<T, E> {
+ fn is_test_result_ok(&self) -> bool {
+ self.is_ok()
+ }
+}
+
+/// Returns whether a test result is to be considered OK.
+///
+/// This will be `assert!`ed from the generated tests.
+#[doc(hidden)]
+#[expect(private_bounds)]
+pub fn is_test_result_ok(t: impl TestResult) -> bool {
+ t.is_test_result_ok()
+}
+
/// Represents an individual test case.
///
/// The [`kunit_unsafe_test_suite!`] macro expects a NULL-terminated list of valid test cases.
diff --git a/rust/macros/kunit.rs b/rust/macros/kunit.rs
index eb4f2afdbe43..9681775d160a 100644
--- a/rust/macros/kunit.rs
+++ b/rust/macros/kunit.rs
@@ -105,8 +105,9 @@ pub(crate) fn kunit_tests(attr: TokenStream, ts: TokenStream) -> TokenStream {
let path = crate::helpers::file();
for test in &tests {
let kunit_wrapper_fn_name = format!("kunit_rust_wrapper_{}", test);
+ // An extra `use` is used here to reduce the length of the message.
let kunit_wrapper = format!(
- "unsafe extern \"C\" fn {}(_test: *mut kernel::bindings::kunit) {{ {}(); }}",
+ "unsafe extern \"C\" fn {}(_test: *mut kernel::bindings::kunit) {{ use kernel::kunit::is_test_result_ok; assert!(is_test_result_ok({}())); }}",
kunit_wrapper_fn_name, test
);
writeln!(kunit_macros, "{kunit_wrapper}").unwrap();
--
2.49.0